<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        class Person {
            static num = 0 ;
            constructor(name,age){
                Person.num ++ ; 
                this.name = name ; 
                this.age = age ;
            }
        }
        let zhangsan = new Person("张三",25);
        let zhangsan2 = new Person("张三",25);
        console.log(Person.num);
    </script>
</body>
</html>